Metal coins which can be distinguished and separated from one another by physical methods responding to magnetic properties

ABSTRACT

In order to make metal disks, especially coins, distinguishable and separable from one another and from disks consisting of other materials on the basis of their magnetic properties, they are made according to the invention of one or more nonmagnetic layers, which consist preferably of a copper-nickel alloy containing 5 to 60 percent nickel, and of one or more layers of magnetic metal, especially nickel, in special, very specific thickness ratios between the magnetic layers and the overall thickness of the metal disks in question.

United States Patent Conradt et al.

[451 Jan.i,w72

METAL COINS WHICH CAN BE DISTINGUISHED AND SEPARATED FROM ONE ANOTHER BY PHYSICAL METHODS RESPONDING TO MAGNETIC PROPERTIES Hans Conradt; Hugo Zoebe, both of Altena, Westphalia, Germany Assignee: Vereinigte Deutsche Metallwerke AG Filed: May 17, 1968 Appl. No.: 729,904

Inventors:

Foreign Application Priority Data Field of Search ..29/194, 199, 183.5

[56] References Cited UNITED STATES PATENTS 3,368,880 2/1968 Turillon ..29/l83.5 3,407,050 10/1968 Trapp ..29/199 Primary Examiner-Byland Bizot AttorneyBurgess, Dinklage & Sprung [57] ABSTRACT In order to make metal disks, especially coins, distinguishable and separable from one another and from disks consisting of other materials on the basis of their magnetic properties, they are made according to the invention of one or more nonmagnetic layers, which consist preferably of a copper-nickel alloy containing 5 to 60 percent nickel, and of one or more layers of magnetic metal, especially nickel, in special, very specific thickness ratios between the magnetic layers and the overall thickness of the metal disks in question.

4 Claims, No Drawings METAL COINS WHICH CAN BE DISTINGUISHED AND SEPARATED FROM ONE ANOTHER BY PHYSICAL METHODS RESPONDING TO MAGNETIC PROPERTIES The application relates to metal disks, especially coins, or roundels to be stamped into coins, which, although of equal thickness and size, are distinguishable and separable from one another by methods based on magnetic properties. Distinguishability by such prior art methods is important for the operation of coin-operated machines, such as those serving for the sale of merchandise, insofar as they make it impossible or considerably more difficult to cheat the machine by the use of imitations that can be obtained cheaply or of coins of other countries and the like.

Coin-operated machines are as a rule set to accept a certain coin. The acceptance of other kinds of coins has to be prevented by the use of certain test devices. These include primarily purely'mechanical devices, which test the coin for size and weight. These qualities, however, are easy to imitate by means of materials of lower value. Since coins usually consist of nonmagnetizable materials, nearly every coin-operated machine, therefore, is also equipped with a device which rejects magnetic materials with the aid of a permanent magnet. This, however, does not enable imitations of lesser value made from the nonmagnetic materials to be always rejected. For this purpose, devices are used in most coin machines which perform the eddy-current test.

The eddy-current test is based on the well-known principle that electrical current is produced in a conductor when it is passed through a magnetic field. In a discoidal electrical conductor, the current thus produced flows in small circular paths as an eddy current. The effect of this eddy current that is important to the eddy-current test consists in the formation of a second magnetic field which opposes the movement of the conductor through the first magnetic field. The result is that the disk slows down when it passes through the magnetic field. Coin-operated machines almost always use the eddy-current test. In this test the metal disks roll on edge in a suitable inclined guiding means on which a magnetic field is arranged in such a manner that the disks cut the magnetic lines of force towards the end of the guide and are directed by deflecting pins, deflecting plates or bouncing anvils into the collection or rejection channel, according to their speed. The final velocity of the metal disk depends on the eddy-current retardation and on its weight. The force due to weight is proportional to the specific weight of the material, if the shape is the same, and the eddy-current retardation is proportional to its conductivity or inversely proportional to its specific electrical resistance. The retarding force opposes the force due to weight. If the length of. the roll path is the same and its inclination is the same, the quotient obtained by dividing the force due to weight by the retarding force, i.e., the product of the specific weight and the specific electrical resistance, is a direct mea sure of the final velocity, since both the magnetic field and the speed of entry are always the same in the same machine.

A perfect separation of disks made of other materials from those intended for the operation of the coin-operated machine would be possible if a material were used for the disks to be accepted by the machine, in which the product of specific weight and electrical resistance differs sharply from the same product in other materials that are suitable as regards the other conditions. However, it has not been possible hitherto to find such a material that is not capable of substitution by other materials. The solution of this problem is further complicated by the fact that most coin-operated machines are set for operation by coins, and coins are required to have other properties, in addition to slot-machine security, the term used to describe the lack of metal disks or lesser value coins that can substitute them.

Coins made of coin silver, i.e., alloys of silver and copper in various percentages, do not provide slot-machine security because the electrical resistance varies only slightly with the composition (ratio of silver to copper). Thus it is possible to use the coins of different countries in slot machines set for silver coins. The problem then is the fact that such coins may differ from one another considerably in value. Even in the same composition, such coins can differ greatly in electrical resistance, and hence in chute travel time, according to the heat treatment given them in the manufacturing process before they are stamped. In coin-operated machines intended for the acceptance of coin silver, therefore, it is necessary to set a very wide range of acceptance. Consequently, it is very easy in this case to use copper-silver alloys of lower value and even technical copper.

In the case of materials having relatively high specific electrical resistances, the separation of adjacently lying materials in the magnetic fields that are available and produced by permanent magnets is very difficult. It requires a very delicate ad- 1 5 justment of the coin tester. Furthermore, even then it will be possible to find easily available materials from which counterfeits can be made. This is the case, for example, with chromium-nickel steels, copper-nickel alloys, brasses, bronzes and silver-copper alloys additionally alloyed with zinc and/or nickel.

Copper plated with copper-nickel has been proposed in connection with slot-machine security, and a certain value for the product of the specific weight and specific electrical resistance plus a certain minimum thickness for the plating has been prescribed for the purpose of improving slot-machine security. Certain technical types of copper, however, are suitable for counterfeiting, so even there slot-machine security is inadequate. Furthermore, plating the harder copper-nickel component onto the soft copper core presents technical difficulties.

Magnetizable materials are not suitable for eddy-current testing because they stick to the permanent magnet. The coin testers in the machines are generally set to reject such materials.

The proposal has already been made to use a coin made of nickel containing 5 percent silicon as a nonmagnetizable material, with a magnetizable core made of a nickel-ironmolybdenum alloy of about percent nickel. This was based on the consideration that a slightly magnetic coin, when it rolls past the magnet of an eddy-current tester, is attracted to the magnet, but does not stick to it. Since the front edge of the coin contacts the magnet, the resultant reduction of speed by friction slows the coin, precisely as it would be retarded by the eddy-current mechanism. It was believed that, if this principle were used, the correct performance of the coin could be achieved only by a very carefully controlled magnetism, and therefore it was believed that the use of a special alloy whose magnetism could be very precisely controlled was a potential answer to the problem. Moreover, it was considered necessary for this purpose to provide a uniform friction surface on all coins so constructed and on the magnet poles of the coin tester, by the application, for example, of a special band in the latter case. Slot-machine security is not assured in the case of coins such as these, either, since they could be substituted on the one hand by all bodies having the same friction effect, and on the other hand by all nonmagnetic materials having an eddy-current effect equivalent to the friction effect.

It is, therefore, an object of this invention to provide a novel disk or coin for use in coin-operated machines, such as vending machines, slot machines, coimoperated laundries and the like.

Another object of this invention resides in a series of novel disks or coins of substantially the same dimensions, which are readily distinguishable from each other by magnetic means.

A further object of this invention resides in such novel disks or coins which meet other physical requirements of coinage.

Other and additional objects of this invention will become apparent from a consideration of this entire specification, including the claims hereof.

In accord with and fulfilling these objects, one aspect of this invention resides in a novel disk or coin having at least one magnetizable component and at least one nonmagnetizable component. There are always at least three (3) layers in each disk according to this invention, with each layer traversing substantially the total disk diameter. Put another way, the disks of this invention are made up of at least three layers which are of substantially equal dimensions in all respects, except for thickness. Of these three layers, two are preferably identical in thickness for all similar denomination disks. It is further preferred that each disk is substantially symmetrical in all respects.

In accord with this invention, the disk has two outer layers and at least one inner core layer. Either the core or the outer layers may be magnetizable. The ratio of total magnetizable layer(s) thickness to total disk thickness is determinative of the denomination of the disk. It is preferred that disks or coins of different denomination have magnetizable layer thicknesses which vary from each other at least about 30 percent, based upon the magnetizable layer thickness.

The invention is based on the recognition that, in the case of such coins or metal disks, the outside of which is made of nonmagnetizable materials but having a magnetizable core, the magnetic attraction produces both an eddy-current retardation and a retardation by the magnetic attraction, which depends on the thickness of the magnetizable core, and the friction forces in this case will be unimportant if the magnetic attraction force is so controlled that the coins do not stick to the retarding magnet, and so that this regulation of the magnetic attraction forces can be performed by regulating the magnetic field and/or the thickness of the magnetizable corei.e., so that it does not depend on the material alone.

This is shown, for example, by the following experiment, which was performed in an eddy-current retarder with disks made of copper-nickel 25 having nickel cores amounting to 2.6%, 4%, 6%, 8.5% and 12% of the total total The magnetic field was created by the installation of weak magnets varying from four to 13 in number.

With four of these magnets, the disk having a l2 percent nickel core was stopped, the disk with the 8.5 percent thick core was passed through with good separation, while the disks having thinner nickel cores, as well as disks made of technical copper and American silver quarters passed through at considerably higher speed. When the magnetic field was slightly weakened by the removal of two magnets or by the interposition of an air gap, the 12 percent nickel disk was passed through with good separation. When six magnets were installed, the disk with 8.5 percent nickel was stopped, and the one with 6 percent nickel rolled at the same speed as, for example, technical copper and American quarters. With nine magnets, the disk duplexed to 4 percent nickel was in the coin silver range; the one duplexed to 2.6 percent nickel was in the region between the silver-frec materials and coin silver. With 13 weak magnets, the rolling time of the disk with 2.6 percent nickel could be adjusted so that it was in the range not covered by other materials. The possibility is thus offered of setting up acceptance ranges which are covered by no other material by adjusting the thickness of the magnetizable layer, which can be maintained relatively precisely in actual production, and by selecting the field strength of the retarding magnet and the distance between the retarding magnet and the coin rolling chute. The smaller core thicknesses up to about 6 percent nickel can be imitated by materials having lower specific electrical resistances, but counterfeiting would be profitable only in the case oflarge coin denominations, on account of the dif ficulties involved.

Due to the fact that the invention makes available metal disks of equal thickness and size, which are made from materials that are not magnetizable and are suitable for the manufacture of coins, and which have a magnetizable core and can be separated or distinguished from one another by known physical methods based on magnetic properties, these coins being characterized according to the invention by the fact that the metal disks to be distinguished or separated from one another have a magnetizable core of variable thickness, and the different thicknesses of the cores are determined within a gradation that is discernible by the said methods, it is made possible for the technical world to manufacture a particular coin that is difficult to counterfeit and offers slot-machine security, or to manufacture an entire coinage having these properties, which hitherto have not been attainable. Such a coinage system is not only available to governments or for a worldwide system of coinage, but it is also available to the individual manufacturer of coin-operated machines or of test devices for such machines. The manufacturer can easily adjust his testers for the acceptance of a disk made available by the invention and sell disks of this kind to his purchasers at the price being charged for the goods obtainable from the machines. One is not bound to the materials named above in the selection of such disks because other combinations of nonmagnetizable and magnetizable materials can be used. In any case, these materials have the additional advantage that the materials that are obtainable in normal commerce, and even the nonmagnetizable materials which are presently in general use for coinage can be reliably separated from the disks on the basis of the difference in magnetic properties if the coin-operated machine is adjusted to the right grade for the difference in core thickness. The correct grading for core thicknesses from I to 50 percent is possible, taking into consideration the technical manufacturing possibilities and the separating ability of the test combining magnetic attraction and eddy-current rctardation. It is therefore desirable to provide the coins or tokens according to the invention with cores whose thicknesses lie in this range.

It has furthermore been found that the manufacturers of coins or of coin blanks can make them easily separable from one another by manufacturing coins having graduated thicknesses within the above-stated range of thicknesses so that the core in each grade is at least 30 percent thicker than the core of the preceding grade.

Whereas any suitable combination of metals in the meaning of the invention can be used for making foolproof slotmachine tokens in private use, the coinage circulated by governments must meet an additional series of other requirements, such as ring, difiicult-to-imitate color, high density, malleability, good stamping and striking qualities, good corrosion resistance, and good resistance to wear after striking. The nonmagnetizable copper-nickel alloys with 5 to 60 percent, preferably [5 to 30 percent nickel content, not only meet all these requirements demanded of a coin alloy but, when combined with nickel cores corresponding to the invention, they constitute coins which offer complete slot-machine security, and when the core thickness is in the indicated range up to 6 percent of the total, they offer at least satisfactory slotmachine security. If desired, the above-named nonmagnetic alloys may contain other elemental components which do not impair plating qualities and do not make the alloys magnetic, such as Zn, Mn, Fe, Si and the like.

If copper-nickel alloys having 5 to 60 percent, and preferably 15 to 30 percent nickel content, are used along with nickel cores in thicknesses of 2.6%, 4%, 6%, 8.5%, l2% and 17% of the total thickness of the disks, a selection of coins will then be available which satisfy all other coinage requirements and which, furthermore, offer a slot-machine security such as has never been known hitherto.

The coins and tokens corresponding to the invention possess the additional advantage that they can be distinguished and separated from one another easily by means of other magnetic and electronic methods, and also from counterfeits made of monmagnetic or strongly magnetic materials. All of the qualities and uses described above are still possible even if the magnetic part of the metal disks according to the invention consists of two layers of equal thickness on the surfaces of same, while the nonmagnetic part serves as the core. Each of the covering layers then needs to be only half as thick for the same purpose as it needs to be in coins and tokens in which the core consists of the magnetic material. A metal disk having a magnetic core having, for example, 2.6 percent of the total thickness of the disk then corresponds to a metal disk having a thickness amounting to L3 percent of the total thickness of the disk in each covering layer, and a metal disk having a magnetic core whose thickness is 4 percent of the total thickness of the disk then corresponds to a disk having magnetic cover layers, each of which has a thickness amounting to 2 percent of the total thickness of the disk, and so forth. Otherwise the conditions that are to be created are precisely the same as in the case of the magnetic-core disks described above.

The advantage of a laminated material having magnetic covering layers of preferably identical thickness lies in a great simplification of the manufacturing process and hence in a reduction of manufacturing costs. The application of thin layers to a thicker core is easier to perform than that of thick layers to a thinner core because of the difference in the deformation which the inner core and the outer layers undergo in the rolling process. Furthermore, the thinner covering layer, especially when made of the pure magnetic metals, such as nickel, can be applied by means of a heavy electroplating. Lastly, cold rolling and annealing operations compress the layers together to such an extent that the bond produced between them is equal to that produced in roll-laminated metals.

However, it is also possible to apply the cover layers by rolling in a laminating mill, either hot or cold.

What is claimed is:

ii. A coin or material from which such coin can be struck consisting of a laminate of at least three layers at least one of which consists of nickel and at least one of which is of coppernickel alloy containing about 5 to 60 weight percent nickel, said nickel and alloy layers being alternately positioned with respect to each other, said nickel layer or layers consisting of about 1 to 50 percent of the thickness of the laminate.

2. A coin or material as claimed in claim 1, consisting essentially of three layers, the center layer of which is nickel, and the two outer layers of which are each said copper-nickel alloy.

3. A coin or material as claimed in claim 1, consisting essentially of three layers, wherein the outer layers thereof are nickel and the core layer thereof is said copper-nickel alloy.

4. A coin or material as claimed in claim 1, wherein said copper'nickel alloy contains about 15 to 30 weight percent nickel. 

2. A coin or material as claimed in claim 1, consisting essentially of three layers, the center layer of which is nickel, and the two outer layers of which are each said copper-nickel alloy.
 3. A coin or material as claimed in claim 1, consisting essentially of three layers, wherein the outer layers thereof are nickel and the core layer thereof is said copper-nickel alloy.
 4. A coin or material as claimed in claim 1, wherein said copper-nickel alloy contains about 15 to 30 weight percent nickel. 